This invention relates to a spindle device. Referring to a well known type of spindle device, in a bearing arrangement of a grinding spindle or a spindle for a lathe or the like, a pair of ball bearings support a shaft in a back to back spaced apart state in positions near a tool or work mounting side (hereinafter referred to as "front side") and remote from the mounting side (hereinafter referred to as "rear side"). In other words, two angular contact bearings are so arranged that the rear edges of the two bearings face each other at a predetermined distance from one another.
FIG. 5 illustrates a conventional spindle device of the afore-mentioned type.
In the drawing, reference numeral 1 denotes a shaft, 2 denotes a tool or work mounting portion and 3 denotes a driving wheel. The shaft 1 is carried by a front side ball bearing 4 (hereinafter referred to as "front bearing") and a rear side ball bearing 5 (hereinafter referred to as "rear bearing"). In these ball bearings, angular contact bearings are arranged in the back to back spaced apart state and a spring 6 is inserted between the two bearings in such a manner as to incur a preload. Rolling elements such as balls 15 are disposed in the respective bearings 4, 5 as illustrated.
However, in such a conventional type of spindle device, axial and radial deviations of several .mu.m degree on the shaft during its running time are unavoidably generated, even if a ball bearing with a high performance is used.
Two reasons have been found why such deviation is generated; one reason is that there exists a slight working aberration in parallel degree between the race way and the thrust side surface of the bearing; and the other reason is that, as shown in FIG. 6, since it is almost impossible to finish a shoulder face 20 on the housing 17 and a shoulder face 21 on the shaft which serve as datum planes when the bearing 4 is mounted on a housing (sleeve) 17 and the shaft 1 so accurately as to intersect perfectly at right angles with respect to the rotary axis X--X' of the spindle, the race way of an outer ring 16 mounted on the housing 17 can not be made perfectly parallel with the race way of an inner ring 14 mounted on the shaft 1, and as the shaft rotates, the deviation from parallel fluctuates, thus generating a sort of cam action.